January 17, 2013

Marine Snail Teeth Inspire Improvement To Nanoscale Materials

A new study led by the University of California, Riverside's Bourns College of Engineering is using the teeth of a coastal California marine snail to create less costly and more efficient nanoscale materials in an effort to improve solar cells and lithium-ion batteries.

Published in the recent issue of Advanced Functional Materials, assistant professor of chemical and environmental engineering David Kisailus' new report details how the teeth of chiton grow.

The study focused on the largest type of chiton, the gumboot chiton, which can be up to a foot long. Found along the shores of the Pacific in a range from central California to Alaska, they have a leathery upper skin that is sometimes reddish-brown and sometimes orange. This has led to the strange nickname of "wandering meatloaf."

Chitons use a specialized rasping organ called the radula, which is a conveyor belt-like structure containing 70 to 80 parallel rows of teeth. During feeding, the first few rows of teeth are used to grind rock to get to the algae growing on it. These teeth become worn, but new teeth are produced and move into the "wear zone" at the same rate that the worn teeth are shed.

Kisailus focuses on nature as inspiration for designing next generation engineering projects and materials. Because he was interested in abrasion and impact-resistant materials, he started studying chitons five years ago. In a previous study, Kisailus determined that the chiton teeth contain the hardest biomineral known on Earth, magnetite, which is the key mineral that not only makes the tooth hard, but also magnetic.

Kisailus and his colleagues from Harvard University, Chapman University and the Brookhaven National Laboratory set out to determine how the hard and magnetic outer region of the tooth forms. Their findings reveal that this occurs in three steps. First, hydrated iron oxide (ferrihydrite) crystals nucleate on a fiber-like complex sugar, or chitonous, organic template. Then, these crystals convert to a magnetic iron oxide (magnetite) through a process called solid-state transformation. Finally, the magnetite particles grow along the organic fibers of the chitonous material, yielding parallel rods within the mature teeth, making them both hard and tough.

“Incredibly, all of this occurs at room temperature and under environmentally benign conditions,” Kisailus said. “This makes it appealing to utilize similar strategies to make nanomaterials in a cost-effective manner.”

In the lab, the team is using the lessons learned from this biomineralization pathway to guide the growth of minerals used in solar cells and lithium-ion batteries. By controlling both the crystal size and the shape and orientation of engineering nanomaterials, Kisailus believes he will be able to build materials that will allow more efficient operation of solar cells and lithium-ion batteries.

The chiton teeth model has another advantages as well: engineering nanocrystals can be grown at significantly lower temperatures, which means significantly lower production costs.

The team claims these same techniques could be used to develop everything from material for cars and plane frames to abrasion resistant clothing. Understanding the formation and properties of chiton teeth could also help to create better oil drills and dental drill bits.